The Milky Way is a spiral galaxy which consists of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. It is surrounded by a much fainter halo of stars, many of which reside in globular clusters. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disk because of the young, hot OB stars that inhabit them.
- The Orion Molecular Cloud Complex extends throughout the constellation of Orion and includes Barnard's Loop, the Horsehead Nebula, Messier 43, Messier 78, and the Flame Nebula. Stars are forming throughout the Orion Nebula, and due to this heat-intensive process the region is particularly prominent in the infrared.
Orion Nebula (M42)Edit
It is s a diffuse nebula situated south of Orion's Belt in the constellation of Orion. It contains a very young open cluster, known as the Trapezium which is made of a total of 6 stars instead of the believed 4. It is estimated to be 24 light years across.
The current astronomical model for the nebula consists of an ionized region roughly centered on Theta1 Orionis C, the star responsible for most of the ultraviolet ionizing radiation.
The dark lane that extends from the north toward the bright region is called the "Fish's Mouth". The illuminated regions to both sides are called the "Wings". Other features include "The Sword", "The Thrust", and "The Sail".
Barnard's Loop (catalogue designation Sh 2-276) is an emission nebula in the constellation of Orion. The loop takes the form of a large arc centred approximately on the Orion Nebula.
The loop extends over about 600 arcminutes, covering much of Orion.
It is estimated to lie at a distance of approximately 1600 light years, giving it actual dimensions of about 300 light years across. It is thought to have originated in a supernova explosion about 2 million years ago, which may have also created several known runaway stars, including AE Aurigae, Mu Columbae and 53 Arietis, which are believed to have been part of a multiple star system in which one component exploded as a supernova.
The Horsehead Nebula is a dark nebula in the constellation Orion. The nebula is located just to the south of the star Alnitak, which is farthest east on Orion's Belt.
The red or pinkish glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma . The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming.
The nebula exhibits a noticeable change in the density of the stars which indicates that a red ribbon of radiant red hydrogen gas at the precipice of a sizable dark cloud. The underside of the horse’s visible ‘neck’ reflects this concept of shade and density because it casts a great shadow across the field of view just below the horse’s ‘muzzle’. A glowing strip of hydrogen gas marks the edge of the massive cloud and noticeable densities of stars are present on either side.
A complex housing forming stars, known as a stellar nursery, can contain over 100 known organic and inorganic gases as well of dust consisting of large and complex organic molecules. The darkness of the massive nebula is not explained by this dust and gas, but by the complex blocking the light of stars behind it. The heavy concentrations of dust in the Horsehead Nebula region and neighbouring Orion Nebula are localized, resulting in alternating sections of nearly complete opacity and transparency.
The Flame Nebula, designated as NGC 2024 and Sh2-277, is an emission nebula in the constellation Orion.
The bright star Alnitak (ζ Ori), the easternmost star in the Belt of Orion, shines energetic ultraviolet light into the Flame and this knocks electrons away from the great clouds of hydrogen gas that reside there. Much of the glow results when the electrons and ionized hydrogen recombine. Additional dark gas and dust lies in front of the bright part of the nebula and this is what causes the dark network that appears in the center of the glowing gas. The Flame Nebula is part of the Orion Molecular Cloud Complex, a star-forming region that includes the famous Horsehead Nebula.
Also known as M43 is an H II region (large, low-density cloud of partially ionized gas in which star formation has recently taken place). in the Orion constellation.
The diffuse nebula M43 surrounds the irregular young "nebula variable" NU Orionis (HD 37061) – a rather cool, young star cooking in a rich HII region. This small star cluster accompanied by an emission/reflection nebula just to the north of the Orion Nebula’s “Trapezium” region is often mistake for part of the great nebula itself, however, M43 contains its own, separate small cluster of stars which have formed in this part of the Orion Nebula.
Messier 78 (also known as M 78 or NGC 2068) is a reflection nebula in the constellation Orion.
M78 is the brightest diffuse reflection nebula of a group of nebulae that include NGC 2064, NGC 2067 and NGC 2071.
These two stars, HD 38563A and HD 38563B, are responsible for making the cloud of dust in M78 visible by reflecting their light.
In and near the nebula M78, 45 low mass stars with hydrogen emission lines, irregular variables of the T Tauri type, young stars still in the process of formation as well as some 17 Herbig-Haro objects are known in M78.